Actuators, such as those used in missile fuel delivery and other time-critical systems, must satisfy high performance requirements. They must begin operation extremely quickly, thereby minimizing the time-delay between receiving a start signal and beginning to operate. They must also complete actuation quickly, minimizing the time between beginning actuation and completing actuation. To meet these high performance requirements, actuators often employ an explosive device to cause actuation. Unfortunately, the gases generated by the explosive device are often forced out of the actuator housing causing contamination of the fuel or gas being controlled by the actuator. In some cases, this contamination can severely degrade overall system performance. In addition, actuators may have to perform effectively after remaining idle in harsh environments for years or even decades.
Seals can be used to minimize the amount of gas that escapes from a pyro-valve actuator. Seals, however, do not generally work effectively. The problem is exacerbated as the seal ages, causing brittleness and shape distortions. Also, due to the high temperatures that result from the explosion, seals can burn and char. Finally, because many seals require lubrication, the lubrication itself can often act as a contaminant—the very problem the seal is attempting to solve.
Interference fits may be able to minimize the amount of blow-by gas that escapes from the actuator. Unfortunately, these devices tend to be expensive, cause drag in the actuator (degrading the unit's performance), require lubrication, and can often cause damage to the actuator itself through galling of metal-to-metal interfaces.
Finally, actuators comprising bellow systems have been developed to contain any gas blow-by that escapes the device. Bellows, however, generally result in increased cost, size, and complexity of the device. Also, the added complexity of bellows generally diminishes the reliability of the device.